1. Field of the Invention
The present invention relates to an inspection method of a compound semiconductor substrate, a compound semiconductor substrate, a surface treatment method of a compound semiconductor substrate, and a method of producing a compound semiconductor crystal, directed to a compound semiconductor substrate having low surface roughness Rms.
2. Description of Related Art
A substrate formed of semiconductor is extensively employed in semiconductor lasers, LEDs (Light Emitting Diode), high-speed devices, and the like by virtue of the light-emitting property and high electron mobility rate. In general, surface treatment is executed to produce a substrate formed of a Group III-V compound semiconductor. For example, Japanese Patent Laying-Open No. 2001-53011 (Patent Document 1) discloses a compound semiconductor having the impurities at the interface between an epitaxial layer and a substrate reduced by optimizing three issues, i.e. the method of washing the substrate, the method of storing the substrate until epitaxial growth is executed, and the conditions for growth prior to initiating epitaxial growth. Patent Document 1 teaches that the oxygen concentration is set to not more than 10 ppm in the method of storage.
Japanese Patent Laying-Open No. 07-201689 (Patent Document 2) discloses a semiconductor wafer with a protection film, having an LB (Langmuir-Blodgett) film formed at the wafer surface. Patent Document 2 also teaches the method of obtaining a clean wafer surface by applying a polymer film on the LB film, and exfoliating the LB film by means of the polymer film.
Japanese Patent Laying-Open No. 05-291371 (Patent Document 3) discloses the method of evaluating the surface of InP semiconductor and interface for estimating the impurity concentration at the surface or interface, by forming a thin InGaAs epitaxial layer at an InP semiconductor substrate and detecting the carrier mobility or carrier concentration.
Japanese Patent Laying-Open No. 2003-86553 (Patent Document 4) discloses a semiconductor crystal wafer rinsed with deionized water at the water temperature of 15° C. or below immediately after polishing to reduce the haze level.
Although the compound semiconductor wafer of Patent Document 1 is stored with the oxygen concentration at 10 ppm or below, approximately 1×1013 oxygen molecules per 1 cc are mixed in such a state. By the presence of such oxygen molecules, oxygen will be adsorbed at the surface of the wafer since the oxygen molecules will collide against the surface of the wafer in an extremely short time. Therefore, there is a problem that impurities at the surface will not be reduced in the substrate storage method disclosed in Patent Document 1.
The semiconductor wafer with a protection film disclosed in Patent Document 2 is produced based on the method of forming an LB film at the wafer surface. It is therefore difficult to completely remove all the atoms constituting the LB film in atomic order. There was a problem that surface-active agents and the like remain on the surface of the wafer. Further, the contact of the polymer film with the surface may cause contamination by particles from the polymer film per se. Additionally, particles or scratches may be generated when the polymer film is exfoliated after contact.
In the evaluation method of the InP semiconductor surface and interface disclosed in Patent Document 3, epitaxial growth must be executed for evaluation. Since the epitaxial layer obtained by epitaxial growth must be of extremely high accuracy, the cleanness of the epitaxial device must be always maintained. Thus, there was a problem that the cost is increased.
For the semiconductor crystal wafer disclosed in Patent Document 4, deionized water of low temperature must be supplied. This means that the deionized water device including an ultraviolet lamp and the like as the heat source must be maintained at a temperature lower than the room temperature. Thus, there is a problem that the cost is increased.
For the semiconductor crystal wafer disclosed in Patent Document 4, the haze level is measured using a mirror reflection type inspection device to obtain an epitaxial layer of high quality. However, the optical scheme allows the detection of only the average of the surface roughness Rms in a scope of an area extremely larger than the size of an atom. Further, the size of the atom is extremely small as compared to the wavelength of light. Therefore, there was a problem that the unevenness of the substrate surface cannot be detected in atomic order.